Fig. 6.

Geniculohypothalamic inputs to the central clock. (A) Schematic of the geniculohypothalamic pathway. The IGL receives dense excitatory input (+) from mRGCs, and GABAergic neurons in this region [including a population that co-expresses neuropeptide Y (NPY)] provide inhibitory input (−) to VIP-rich portions of the SCN. (B) The normalised (according to maximal firing) sensitivity of cells in the mouse IGL region to light steps providing equal activation of all photoreceptor classes. The data reveal substantially larger responses to low light levels than those shown by SCN cells tested under equivalent conditions. (C) Responses of ‘antagonistic’ cells in the IGL region (similar to those reported for some SCN-projecting cells) that selectively respond to illumination of just one eye, with little response to binocular illumination. Periods of darkness are indicated by grey backgrounds and periods of light are indicated by white backgrounds. IGL data in B and C are derived from data presented in Howarth et al. (2014) and SCN sensitivity from Walmsley and Brown (2015).